This invention relates to a power steering pump for an automotive vehicle and, more particularly, to a power steering pump that includes a cam plate accurately located within a housing.
A power steering system of an automotive vehicle comprises a pump for supplying hydraulic fluid under pressure to a power steering gear assembly. A typical power steering pump comprises a rotor having retractable vanes and rotating within a cam chamber. The circumference of the cam chamber is defined by a cam plate that is interposed between upper and lower pressure plates and assembled within a housing. The housing is connected to the steering gear assembly for receiving spent fluid. Suction passages within the housing convey the fluid to inlets to the cam chamber formed in the pressure plates. Pressurized fluid is discharged through outlets in the pressure plate to discharge passages that are connected to the gear assembly. Typically, a flow control assembly regulates the output from the pump and recycles excess fluid through a bypass port to the suction passages. During operation, the rotor is driven by the engine through a belt and pulley mechanism. The rotor draws fluid from the suction passage through the inlets, compresses the fluid, and discharges pressurized fluid through the outlets to the discharge passages that lead to the steering gear assembly.
The cam plate must be accurately aligned in the housing to register the cam chamber with the inlets and outlets. This is typically accomplished by alignment pins extending through bores in the cam plate, or between the perimeter of the cam plate and the housing. Furthermore, the cam chamber typically includes two inlet regions for receiving low pressure fluid and two outlet regions for discharging high pressure fluid. The outlet regions are diametrically arranged to balance the forces created by the high pressure fluid, and similarly the inlet regions are diametrically arranged. In general, it is desired to minimize the radial width of the cam plate to reduce the weight and cost of the pump. However, because of the high pressure of the fluid at the outlet regions, which may exceed 2,500 psi, and the differences in pressures with the inlet regions, forces develop within the cam plate that tend to distort the cam chamber, or even create stresses that may cause catastrophic fracture of the plate. Also, vibration of the cam plate during operation results in noise. Moreover, pressure distortion of the cam plate, and vibration of the alignment pins, increases the noise emanating from the pump.
Therefore, a need exists for a power steering pump that includes a cam plate that is accurately aligned within the pump housing to register the cam chamber with the inlets and outlets, and further that is able to reduce vibration and noise, including noise due to vibration of the cam plate and distortion of the cam chamber. There is also a need to reduce the size and number of components of the pump, while minimizing the vibration and noise, to thereby reduce the size and cost of the pump.
This invention provides a power steering pump for an automotive vehicle that includes a housing having an inner housing wall about an axis, and a cam plate received in the housing. The cam plate defines a cam chamber and includes an perimeter spaced apart from the inner housing wall. The pump also includes a rotor coaxially received in the cam chamber and comprising retractable vanes that cooperate with the cam chamber to pressurize fluid. One or more outlets communicate with the cam chamber for discharging pressurized fluid. In accordance with this invention, the inner housing wall includes an axial groove and the cam plate includes a locator rib received in the groove. The groove and rib are disposed adjacent the outlet port. In the absence of pressurized fluid within the cam chamber, the outer surface of the cam plate about the rib is radially spaced apart from the housing inner surface by a first dimension, and the rib is radially spaced apart from the groove by a second dimension that is less than the first dimension. During operation, the retractable vanes of the rotor cooperate with the cam chamber to pressure fluid adjacent the outlet port. Distortion of the cam plate due to operating fluid pressures directs the rib into a locking engagement within the groove, while maintaining clearance between the housing and the remainder of the cam plate outer surface. This not only accurately positions the cam plate within the housing, but also, secures the cam plate to reduce vibration. Also, the remaining clearance inhibits vibration propagation from the cam plate to the housing. Thus, this invention provides a power steering pump that exhibits reduced noise during operation.